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Thread: Fluke 114 DMM, accurate enough for Lith-ions?

  1. #1

    Default Fluke 114 DMM, accurate enough for Lith-ions?

    Thanks!! If it is, this will be the DMM I'll order!

  2. #2
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    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Quote Originally Posted by lrp View Post
    Thanks!! If it is, this will be the DMM I'll order!
    More than enough, at 4.2 volt the error will be below +/- 0.023 volt.

    But it does not have current ranges.
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  3. #3

    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    I disagree. True that the usual charging termination spec is 4.20V +/-0.05V, so that an error of 0.023V is within that range. But if you are more conservative than that and want to keep the charge voltage at 4.20V max, then the Fluke 114 accuracy is not sufficient to determine that. You don't know if a reading of 4.200V is 4.223V or 4.177V.

    At that price, why not look into the Protek D620 at Circuit Specialists.

  4. #4

    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Range/Resolution: 6.000 V / 0.001 V
    Range/Resolution: 60.00 V / 0.01 V
    Range/Resolution: 600.00 V / 0.1 V
    Accuracy: Ī ([% of reading] + [counts]): 0.5% + 2
    http://us.fluke.com/usen/Products/Fl...(FlukeProducts)
    Last edited by alpg88; 07-21-2009 at 12:23 PM.

  5. #5
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    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Quote Originally Posted by Justin Case View Post
    I disagree. True that the usual charging termination spec is 4.20V +/-0.05V, so that an error of 0.023V is within that range. But if you are more conservative than that and want to keep the charge voltage at 4.20V max, then the Fluke 114 accuracy is not sufficient to determine that. You don't know if a reading of 4.200V is 4.223V or 4.177V.

    At that price, why not look into the Protek D620 at Circuit Specialists.
    I, however, agree with HKJ that it's good enough. The difference in lifespan of a lithium ion cell charged to 4.200V vs 4.223V is small enough that you'd never notice it in normal flashlight use. Also, unless you're monitoring cell voltage with your DMM during charging to make sure you stop at exactly 4.200V, you're at the mercy of the cutoff of the charger as to when charging stops.

    @ lrp: See, that's why the internet is so great. You can get two diametrically opposed answers from complete strangers in a matter of hours.

  6. #6

    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Quote Originally Posted by lrp View Post
    Thanks!! If it is, this will be the DMM I'll order!
    I have to ask. Is this something you need for your job or some other serious use or is it just something you'll be getting to casually check voltages on your rechargeable batteries? Please forgive me as I'm very new to flashlights and don't mean to offend. Also, I understand everyone places different value on items and what is expensive to one person is not that expensive to another. With that said, I'm also looking for a cheap (to me) multimeter for simple, casual hobby use and checking voltages on rechargeable batteries in the future. For the life of me I can't get my mind around spending $100+ on a DMM for casual use. If I was using it for my job, etc then it wouldn't be an issue. But for casual use I just have a hard time with it but maybe that's just me. Does one really need to spend this kind of money on a DMM for casual use to get an acceptable level of accuracy?

    As for the issue regarding the accuracy, if I'm looking for 4.2 volts on a battery and the reading could be 4.177 or 4.223 because of the margin of error, is this not accurate enough?? If the voltage is really 4.177 are you going to put it back on the charger to eek out that 3 hundredths of a volt? Again, I don't mean to offend anyone. I'm still learning and want to understand the 'why' on some of this stuff.

  7. #7

    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    If the voltage is really 4.177V, I probably wouldn't bother putting it back on the charger. But if I got 4.223V hot off the charger, then I personally would get a different charger. One doesn't have to monitor voltage during charging to identify what I would consider an unsat charger that goes above 4.20V.

    My point, which was missed, is that the Fluke 114 might be good enough. I cannot agree that it is good enough. I didn't say that the Fluke was categorically not good enough. It depends on your requirements for things like cycle life, capacity, and even perhaps how capacity changes with charge cycles.

    See this reference, for example:

    http://powerelectronics.com/portable...ttery-life.pdf

    Also, let's say you are willing to tolerate 4.223V terminating voltage. Well, what is the true voltage? Is it as low as 4.200V or as high as 4.246V? Now the upper limit is getting to a non-trivial overvoltage IMO.
    Last edited by Justin Case; 07-21-2009 at 02:09 PM.

  8. #8

    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Its not good enough because at some point in time you really want to measure the current through the battery into your load and you have no ammeter with that unit at all. Measuring current through the batteries into the load with a fresh charge on it typically tells you more about the battery and of course how well your item being run by the battery is working. In the case of LED flashlights, you will get to the point where you want to know the turn on current and current draw when the battery are fresh or are mostly discharged. A voltmeter is not enough. You want a good multimeter that can also measure current up to 10A scale accurately. So pretty soon you will be wishing you had a completely different meter anyway.

  9. #9
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    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    I'm moving this thread to the Batteries/Electronics section where it belongs.
    Resistance is futile...

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    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Quote Originally Posted by Justin Case View Post
    Also, let's say you are willing to tolerate 4.223V terminating voltage. Well, what is the true voltage? Is it as low as 4.200V or as high as 4.246V? Now the upper limit is getting to a non-trivial overvoltage IMO.
    If the Fluke in question read 4.200V, and was off by the specified maximum of +0.023V, then at most you'd be have a 4.223V termination. 4.223V is not too bad in the grand scheme of things for a lithium ion cell.

    From the PDF you linked, there's a curve showing cycle life vs float voltage. 4.200V vs 4.250V give 500 cycles and ~400 cycles to 80% initial capacity respectively, with 4.250V having 5% more capacity to start with than 4.200V charging. Would you notice 400 vs 500 cycles? Maybe. Would you notice 5% more capacity per charge? Maybe. Is 4.250V unsafe as a termination voltage? No.

    More important is the fact that 4.200V is not an absolute for lithium ion cells. Depending additives and other active components, 4.100V might be the termination voltage needed to reach 500 cycles to 80% capacity, or 4.300V might be okay. There are too many variables to make worrying about 0.023V worthwhile.

    The Fluke meter would allow checking of cells to make sure they weren't horribly over charged or over discharged. It seems that's all the OP is looking for.

  11. #11

    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    IMO, overpriced for the given ccuracy specs. Also, no amps measurement capability to measure things like tail current and driver output current. I think there are better choices.

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    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Quote Originally Posted by Justin Case View Post
    IMO, overpriced for the given ccuracy specs. Also, no amps measurement capability to measure things like tail current and driver output current. I think there are better choices.
    It is a bit like buying SureFire or from DX.

    Fluke is not the cheapest or best specified meters, but they are very dependable.
    My website with flashlight, battery and charger information: lygte-info.
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  13. #13

    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    I know Fluke meters are great (I have one, among others), but I just don't see the need to outlay the kind of cash it requires to get into the Fluke club when being used for flashaholic related stuff.

    Here's a great deal for $139 US, and does just about everything a budding flashaholic could want, or need. As far as I can tell, the Protek is $10 US more than the Fluke, but it does so much more.
    http://www.circuitspecialists.com/prod.itml/icOid/9052
    Last edited by clintb; 07-21-2009 at 06:20 PM.

  14. #14

    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Quote Originally Posted by MorePower View Post
    If the Fluke in question read 4.200V, and was off by the specified maximum of +0.023V, then at most you'd be have a 4.223V termination. 4.223V is not too bad in the grand scheme of things for a lithium ion cell.

    From the PDF you linked, there's a curve showing cycle life vs float voltage. 4.200V vs 4.250V give 500 cycles and ~400 cycles to 80% initial capacity respectively, with 4.250V having 5% more capacity to start with than 4.200V charging. Would you notice 400 vs 500 cycles? Maybe. Would you notice 5% more capacity per charge? Maybe. Is 4.250V unsafe as a termination voltage? No.

    More important is the fact that 4.200V is not an absolute for lithium ion cells. Depending additives and other active components, 4.100V might be the termination voltage needed to reach 500 cycles to 80% capacity, or 4.300V might be okay. There are too many variables to make worrying about 0.023V worthwhile.

    The Fluke meter would allow checking of cells to make sure they weren't horribly over charged or over discharged. It seems that's all the OP is looking for.
    My point was that if the DMM reads 4.223V, apparently that is still satisfactory for you. But due to the relatively poor 0.5% range accuracy of this Fluke, the reading could be as high as 4.246V.

    "Horribly" overcharged is in the eye of the beholder. I am unsatisfied with a charger that goes over 4.20V. For me, it's binary. It's either go or no-go. So I want a meter that can differentiate between 4.20V vs. 4.21V or 4.22V or 4.23V. I don't mind paying the price for a good Fluke like an 87-V, but I also expect accuracy specs better than that for a cheap DMM from Harbor Freight. An 0.5% range error simply doesn't cut it. The saving grace for the 114 is that it has a 6,000 count display. Otherwise, the high range error plus the 2 digits of offset error would really kill it.

    The curves in the referenced PDF are notional, since different Li-ion chemistries have different performance. It is precisely because there are so many variables that I would want to eliminate the one variable I can control -- voltage measurement accuracy. And it just so happens that it is an important variable.

    Now, you may still get this Fluke 114 and also combine it with a voltage reference such as the one from Malone Electronics. That can then give you a solid idea as to what the measurement error is. But until then, you just don't know. Does that matter? It does to me. It doesn't for others.
    Last edited by Justin Case; 07-21-2009 at 07:14 PM.

  15. #15

    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Quote Originally Posted by HKJ View Post
    It is a bit like buying SureFire or from DX.

    Fluke is not the cheapest or best specified meters, but they are very dependable.
    Ok, overpriced for the accuracy spec, but at least reliably overpriced and inaccurate. But still sadly limited in functionality since it can't measure current, which is another important measurement in characterizing flashlight performance.

    I suggested the same Protek D620 meter from Circuit Specialists that clintb did.
    Last edited by Justin Case; 07-21-2009 at 07:07 PM.

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    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    > For me, it's binary. It's either go or no-go.

    You're measuring a fundamentally chemical reaction. It isn't binary. The reaction is logarithmic.

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    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    As I was on the market for a DMM as well, I dare to share my humbly opinion.

    Accuracy:
    The advertised specs reminds me somehow to advertising lumens for a flashlight;
    youíll never know if they are correct.
    For a better accuracy, you want to calibrate your DMM or at least
    compare it to a well calibrated meter.

    Fluke:
    Fluke is nice but incredibly expansive if not to say overpriced.
    The 11x series is considered entry-level.
    E.g. on a plant/ lab the Fluke 114 would be the meter you would hand out
    to a trainee to make sure he donít kill himself while measuring (CAT IV 600V and no current setting)
    and that you donít have to buy him a new meter every week.
    If you want to go the Fluke way for precise electronic measuerement,
    you will have to invest even more. Iíd say the Fluke 175 is the entry level for that purpose.

    Does it make sense to buy a Fluke to check batteries?
    IMHO, not just no, but absolutely no.
    These meters are for the pros or die hard electronic geeks.
    You will pay for a lot of things that you will never need,
    like brand name, compliance and certification for a lot of standards, and the like.
    In addition, a high price doesnít necessarily mean higher accuracy here. (see above)
    Further, voltage measuring is easy to implement, so every reasonable DMM would do a good job here.

    So what would I recommend:
    - As no one can rule out the possibility completely, that the meter will be used some day for
    high voltage measurements, the DMM should at least comply with CAT III / 600V.
    (better save than sorrow)
    - The current ports have to be protected by fuses.
    - Accuracy for voltage reading should be 0,5% or better.
    To compare the accuracy between DMMs according to the specs,
    rather look at the current settings.
    - Seeing all the nice charts here at CPF, you may get inspired to do some chart yourself,
    so maybe consider to get a DMM with a data logger.
    - A temperature setting may be useful as well.

    If you want a known/respected brand, maybe Amprobe is the better choice for your purpose.
    May take a look at the 38XR-A (data logger) or the 37XR-A.

    As an alternative to the recommendations above, maybe also take a look at Uni-Trend.

    http://www.uni-trend.com/

    I canít say much about the quality yet, as I just ordered one. (UT71C)
    The specs are promising though.

    If you donít need all these bells and whistles, I dare to say, every not too shabby
    DMM in the $50-$80 price range will do a good job for checking batteries.

    Hope that helps somehow
    Thomas

  18. #18

    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Quote Originally Posted by Scott Packard View Post
    > For me, it's binary. It's either go or no-go.

    You're measuring a fundamentally chemical reaction. It isn't binary. The reaction is logarithmic.
    So what. If the charger uses a terminating voltage over 4.20V, I get rid of it. That's my binary decision.
    Last edited by Justin Case; 07-22-2009 at 05:27 AM.

  19. #19

    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    When it comes to tools and measuring equipment, get the best you can afford.
    It is for life !

    Current, Temp, RMS, frequency. Yes if you are serious about the hobby.
    Now if it is just to check a battery condition ?

    And as said above, when it comes to electric equipment, poorly insulated or poorly protected equipment may lead to your life being short circuit!


    And please, do some learning about it. I am amazed how basic things like voltage, intensity etc... seems to be mysterious while every 16 years old should know about !

    Isn't it part of basic education anymore ?

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    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    If you are looking for information regarding multimeter accuracy then you better to be prepared spending some cash. Seriously, don't go the cheap route, you will just end up with more meters.

    If you are looking at a Fluke, then I suggest not a Fluke 114 because it's just not economical for the 0.5% basic dc accuracy. Spend a little bit more, and get one with 0.1% or lower.

    As mention above, Uni-Trend is a very dependable and reliable brand. They are probably the biggest monopoly in the multimeter market. Uni-Trend is a contractor and make many and most rebranded, for example Tenma.

    I have a UT71D and it's has a DC volt accuracy of 0.025% which matches my Fluke 187. I haven't found any unacceptable drift over the pass two years since I bought it. This is based on one sample that I have. However, the UT71D is not cheap. I'm not saying you should buy a Uni-Trend here, I find some other measurements a little unstable when there's noise. It takes a while(10-15sec) for the Uni-Trend to settle down when measuring capacitance. The Fluke always give an accurate result and the measurement is repeatable.

    Last edited by koala; 07-22-2009 at 07:50 AM.
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    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Sheesh, all you flashoholics worrying about 1/10000 Volt
    Don't forget the resistors in your flashlight are at most 1%

  22. #22

    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Thanks guys! I really would only be using it for checking Lith-ion batteries, I just want a meter to be accurate for this task only. What other meters would do the job well?

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    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Quote Originally Posted by lrp View Post
    Thanks guys! I really would only be using it for checking Lith-ion batteries, I just want a meter to be accurate for this task only. What other meters would do the job well?
    Almost any meter will do, but it is niece to have a meter with 5000 or 6000 display, because you get a extra digit in the readout.
    I.e. with a 2000/3000/4000 display you will get: 4.21, but a 5000/6000 display can show 4.207.

    It is not that important if the precision is 0.5% or 0.05%, as long as you are checking for a max. of 4.2 volt, the small errors in the readout will only affect the number of cycles the battery can be used, not making it dangerous in any way. And as long as you do not have the specification for the actual battery chemistry, you do not know exactly what voltages to check for anyway.

    When checking the specifications for a meter, remember to check for what temperature the meter has to used within for the tolerances to be valid and how long the tolerances are guaranteed to be valid (This is usual a year). For AC measurements the tolerances also needs to include a frequency specification. If any of the above specifications are missing, the tolerance specifications are suspicious.
    Also remember that serious tolerance specifications are maximum errors, that you might encounter if you are using the meter to the limit, not the typical error you get from a meter always keeps on the desktop (At least that is valid for the better meters).

    One important specification (At least for me): The meter must warn about low battery, and not displays a wrong value.
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  24. #24

    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Quote Originally Posted by HKJ View Post
    Almost any meter will do, but it is niece to have a meter with 5000 or 6000 display, because you get a extra digit in the readout.
    I.e. with a 2000/3000/4000 display you will get: 4.21, but a 5000/6000 display can show 4.207.

    Almost any meter will do, but it is niece to have a meter with 5000 or 6000 display, because you get a extra digit in the readout.
    I.e. with a 2000/3000/4000 display you will get: 4.21, but a 5000/6000 display can show 4.207.

    It is not that important if the precision is 0.5% or 0.05%, as long as you are checking for a max. of 4.2 volt, the small errors in the readout will only affect the number of cycles the battery can be used, not making it dangerous in any way. And as long as you do not have the specification for the actual battery chemistry, you do not know exactly what voltages to check for anyway.
    Again, opinions differ on this point. If you get a 4000 digit display DMM or less, then a combination of high range (gain) error and offset error (the digits) can result in IMO fairly high error. The offset error can have a big impact on these low digit DMMs, even if you have a low gain error. Yes, it will probably be safe, but IMO the confidence in the measurement accuracy is not good.

    Let's say you get a DMM with an accuracy of 0.5% + 2 digits like this Fluke 114, except you settle for a 4000 count DMM.

    Then a 4.20V measurement can range from 4.16V to 4.24V. For me, the potential that the voltage can be as high as 4.24V sucks.

    Because of how the digits error works, it is highly doubtful that a low count DMM will read 4.21V vs. a high count DMM at 4.207V, unlike in your hypothetical example. Your example would occur only if there were zero digits of error. More likely, both DMMs will have similar accuracy specs, e.g., +/-(0.5%+2 digits). For a low count DMM (e.g., 3000), the 2 digits go into the hundredths place. For a high count DMM (e.g., 6000 counts), the 2 digits go into the thousandths place. Big difference.

    Yes, there is probably a statistical distribution for the DMM accuracy, and most DMMs will not be in the error extremes. But unless you can calibrate the DMM, compare it to a known accurate DMM, or obtain a voltage reference standard, you don't know where your DMM is in that distribution.

    At a minimum, to reduce the impact of the offset error, I would get a DMM with a display of at least 5000 counts. If the DMM I like (perhaps because it has other useful features) has a relatively high gain error (e.g., 0.5% or more), I would also get a 4.0960V voltage reference from Malone Electronics.

    IMO, you will quickly learn how useful a DMM is and discover all sorts of uses. If you get essentially what is a fairly limited DMM (both in features and accuracy), you will soon wish you had gotten something better.
    Last edited by Justin Case; 07-22-2009 at 11:31 AM.

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    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Quote Originally Posted by Justin Case View Post
    Then a 4.20V measurement can range from 4.16V to 4.24V. For me, the potential that the voltage can be as high as 4.24V sucks.
    You might not like this tolerance, but it is good enough to be safe, to get a decent number of charge cycles from the batteries and to check how much of the charge is left.
    More exact measurement might be nice, but you do not really get any more useful information from it: You will not be safer, the number charge cycles depends on the exact chemistry in the battery, without knowing that, you voltage reading does not help you, and the charge left will not be more exact and even if it was, if would probably be irrelevant (Who cares if the light can run 20 or 21 minutes on the remaining charge?).

    Quote Originally Posted by Justin Case View Post
    Yes, there is probably a statistical distribution for the DMM accuracy, and most DMMs will not be in the error extremes. But unless you can calibrate the DMM, compare it to a known accurate DMM, or obtain a voltage reference standard, you don't know where your DMM is in that distribution.
    The error specification does not really work that way, the meter has to be much better calibrated from the factory. Then after being overloaded, being frozen, being boiled, etc. for a year, it must still be within tolerances.

    That is the reason I believe that temperature tolerances and calibration time are important. It is very easy and cheap to make a meter that has 0.01% tolerance when leaving the factory (Thanks to microprocessors and EEPROMS), but can it keep this tolerance, that is the challenge.
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  26. #26
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    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Irp, if you want a Fluke and you're a flashaholic, you should at least get the Fluke 115. As MrGman says, you will want to be able to measure current.

  27. #27

    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Quote Originally Posted by HKJ View Post
    You might not like this tolerance, but it is good enough to be safe, to get a decent number of charge cycles from the batteries and to check how much of the charge is left.
    More exact measurement might be nice, but you do not really get any more useful information from it: You will not be safer, the number charge cycles depends on the exact chemistry in the battery, without knowing that, you voltage reading does not help you, and the charge left will not be more exact and even if it was, if would probably be irrelevant (Who cares if the light can run 20 or 21 minutes on the remaining charge?).



    The error specification does not really work that way, the meter has to be much better calibrated from the factory. Then after being overloaded, being frozen, being boiled, etc. for a year, it must still be within tolerances.

    That is the reason I believe that temperature tolerances and calibration time are important. It is very easy and cheap to make a meter that has 0.01% tolerance when leaving the factory (Thanks to microprocessors and EEPROMS), but can it keep this tolerance, that is the challenge.
    I never said that there was a benefit with being safer if you had a more accurate DMM. As for cycle life, of course you will get better cycle life if you keep the float voltage lower. Even if you don't know the exact Li-ion chemistry, it doesn't really matter. It is the same battery, and thus the chemistry is held constant. If you have a accurate DMM that allows you to differentiate 4.20V from 4.24V, and you make sure that your charger goes only up to 4.20V, you will get better cycle life than if you went to 4.24V. Now you may not know exactly how many more cycles you might get because that is chemistry-dependent, but you will get more with the lower float voltage.

    As for capacity, I have no idea if someone cares about whatever small amount capacity difference might result from the DMM's voltage measurement error. I agree that it is a small amount. But I don't presume that my opinion of that issue applies to anyone else either.

    The issue of ruggedness is an entirely different matter than the paper spec for measurement accuracy, which is what I had been addressing.

    The error spec most certainly works the way I described for the Fluke 114. With a 4.096V reference source, you are about as close to 4.20V as reasonably possible with an easily-obtained, commercial voltage reference. The Fluke will not use a different voltage range so any internal voltage divider circuitry issues don't apply here. Thus, whatever voltage error you measure for the 4.096V reference can be directly applied to your 4.20V measurement. If you are unconcerned about voltage measurement errors of 0.04V for Li-ion OCV, then any error using the above approach is far smaller than that.

  28. #28
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    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Quote Originally Posted by Justin Case View Post
    If you have a accurate DMM that allows you to differentiate 4.20V from 4.24V, and you make sure that your charger goes only up to 4.20V, you will get better cycle life than if you went to 4.24V. Now you may not know exactly how many more cycles you might get because that is chemistry-dependent, but you will get more with the lower float voltage.
    You will also get a better cycle life if yo charge to 4.1 or 4.15 volt, it has nothing to do with the tolerances of the meter.


    As for capacity, I have no idea if someone cares about whatever small amount capacity difference might result from the DMM's voltage measurement error. I agree that it is a small amount. But I don't presume that my opinion of that issue applies to anyone else either.

    Quote Originally Posted by Justin Case View Post
    The error spec most certainly works the way I described for the Fluke 114.
    Have you measured some Fluke 114? I would expect them to be much better than 0.5% from factory, as I described above.

    Quote Originally Posted by Justin Case View Post
    With a 4.096V reference source, you are about as close to 4.20V as reasonably possible with an easily-obtained, commercial voltage reference. The Fluke will not use a different voltage range so any internal voltage divider circuitry issues don't apply here. Thus, whatever voltage error you measure for the 4.096V reference can be directly applied to your 4.20V measurement. If you are unconcerned about voltage measurement errors of 0.04V for Li-ion OCV, then any error using the above approach is far smaller than that.
    Checking the meter against a reference is a very good idea, you just has to know which one has the lowest tolerance, at least if they disagree . But that reference is only good for one voltage range (Which is enough for checking LiIon), that is very far from being enough to verify a modern multimeter. The fact that DC voltage is correct does not in any way prove that any of the other ranges are correct.
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  29. #29

    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Quote Originally Posted by HKJ View Post
    You will also get a better cycle life if yo charge to 4.1 or 4.15 volt, it has nothing to do with the tolerances of the meter.

    Have you measured some Fluke 114? I would expect them to be much better than 0.5% from factory, as I described above.

    Checking the meter against a reference is a very good idea, you just has to know which one has the lowest tolerance, at least if they disagree . But that reference is only good for one voltage range (Which is enough for checking LiIon), that is very far from being enough to verify a modern multimeter. The fact that DC voltage is correct does not in any way prove that any of the other ranges are correct.
    Of course the float voltage (and thus cycle life) has something to do with the accuracy of the meter. With an accurate meter, you know where you stand wrt your charger's terminating (float) voltage. With an inaccurate meter, you don't.

    No I have not measured any statistically valid number of Fluke 114 samples. Have you? Regardless, you don't believe that manufactured products have a statistical distribution for their performance? I clearly said that most DMMs won't be at the extremes of the accuracy spec, which is what you seem to be saying. So what exactly is your complaint? Do you believe that all DMMs will have exactly the same accuracy out of the factory -- essentially a delta function distribution? That's still a statistical distribution.

    I never said that comparing a DMM's measurement at a single voltage was sufficient for any of the other of the DMM's voltage ranges. The point of suggesting the 4.096V reference was to address the OP's interest in checking Li-ions. Malone Electronics checks their voltage references using a calibrated 8.5 digit HP3458A DMM. They also offer a re-cal service. If you have sources for higher voltage references so that other, higher DMM voltage ranges can be checked, speak up.
    Last edited by Justin Case; 07-22-2009 at 12:52 PM.

  30. #30
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    Default Re: Fluke 114 DMM, accurate enough for Lith-ions?

    Quote Originally Posted by Justin Case View Post
    Of course the float voltage (and thus cycle life) has something to do with the accuracy of the meter. With an accurate meter, you know where you stand wrt your charger's terminating (float) voltage. With an inaccurate meter, you don't.
    No, it has not, it has to do with the chemistry in the battery, you do not know if a battery needs 4.20 or 4.15 volt to last 500 cycles, you only know that a lower voltage will give more cycles.


    Quote Originally Posted by Justin Case View Post
    No I have not measured any statistically valid number of Fluke 114 samples. Have you? Regardless, you don't believe that manufactured products have a statistical distribution for their performance? I clearly said that most DMMs won't be at the extremes of the accuracy spec, which is what you seem to be saying. So what exactly is your complaint? Do you believe that all DMMs will have exactly the same accuracy out of the factory -- essentially a delta function distribution? That's still a statistical distribution.
    I agree that the calibration is a statistical distribution, probably a bell curve, but it does not stretch to the limit of the tolerance specifications, it is much more narrow, because much of the tolerance is needed for aging of the components.
    I suspect that many cheap meters are forgetting that in their tolerances, but I have never made a study of it.

    Quote Originally Posted by Justin Case View Post
    If you have sources for higher voltage references so that other, higher DMM voltage ranges can be checked, speak up.
    Fluke 9100 (Sorry, that is a bad joke).
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